Welcome, Guest. Please login or register.
Amiga Kit Amiga Store Iridium Banner AMIStore App Store A1200/A600 4xIDE Interface

AuthorTopic: Different AGNUSes 8372 vs 8375  (Read 495 times)

0 Members and 1 Guest are viewing this topic.

Offline Tumbleweed

Different AGNUSes 8372 vs 8375
« on: June 21, 2022, 04:42:28 PM »
What the difference between the different versions of AGNUS?

There's alot of info on the web and across various Amiga forums but seems there is a lot of misinformation out there as well. The Big Book Of Amiga Hardware shows:

Chip Name   Chip Number   Part Number   Used In
Agnus (512K)   8361   252125-01   A1000 (NTSC), A2000A (NTSC)
Agnus (512K)   8361 R3       A1000(NTSC), A2000A(NTSC)
Agnus (512K)   8367   252362-01   A1000 (PAL), A2000A (PAL)
Agnus (512K)   8370   318070-01   A500 (NTSC), A2000 (NTSC)
Agnus (512K)   8371   318071-01   A500 (PAL), A2000 (PAL)
Agnus (1MB)   8372   318069-02   A500 (PAL), A2000 (PAL) Regular Type
Agnus (1MB)   8372A   318069-029   A500 (PAL), A2000 (PAL) (changed after some damage)
Agnus (2MB)   8372AB   318069-03   A3000 (PAL), A3000T (PAL)
Agnus (2MB)   8372B   318069-03   MegAChip (NTSC)
Agnus (2MB)   8375 R0   318069-18   A500+ (PAL), A600 (PAL)
Agnus (1MB)   8375 / 8375 R1   318069-16   A500 (PAL), A2000 (PAL)
Agnus (2MB)   8375 R2   318069-10   A500+ (PAL), A600 (PAL)
Agnus (2MB)   8375   318069-11   A500+(NTSC) and A600(NTSC)
Agnus (1MB)   8375   318069-17   A500 (NTSC), A2000 (NTSC)
Agnus (2MB)   8375   318069-19   A3000 (NTSC), A3000T (NTSC)
Agnus (2MB)   8375   390544-01   A500+ (PAL), A600 (PAL)
Agnus (2MB)   8375   390544-02   A500+ (NTSC), A600 (NTSC)

My question is can I run a 8375 Agnus [Agnus (2MB)   8375   318069-19   A3000 (NTSC), A3000T (NTSC)] in my A3000T which is fitted with a 8372 Agnus [Agnus (2MB)   8372AB   318069-03   A3000 (PAL), A3000T (PAL)]

And if so what are the advantages?

Weed
A3000T, Cybervision64, CSMKII 060; A3000D, PicassoII, Z3 Fastlane; A2000D, 040, PicassoII; A4000D, A1200, Blizzard 030 MKIV - both not working :(
 

Offline Matt_H

Re: Different AGNUSes 8372 vs 8375
« Reply #1 on: June 21, 2022, 11:27:00 PM »
If you have a 2MB Agnus in your machine that works, why replace it?

My understanding is that the only differences between Agnus (apart from 512K/1MB/2MB) are for compatibility and that there are no performance differences.

Best information is probably to go right to the source: see if you can find a PDF of a Commodore parts catalog and look up the different part numbers.
 

Offline Tumbleweed

Re: Different AGNUSes 8372 vs 8375
« Reply #2 on: June 22, 2022, 07:14:15 AM »
Cheers Matt.

Seems BBoH is missing entries. I found that there is a 8375 Agnes (PAL) version for the 3000T:

Agnus (2MB) 8375 318069-18 A3000 (PAL), A3000T (PAL)

Ill do more digging - its the compatibility aspect I'm interested in. As I understand it Agnes has a part to play in DMA - do the later revisions of the chip improve the stability of DMA?

Weed
A3000T, Cybervision64, CSMKII 060; A3000D, PicassoII, Z3 Fastlane; A2000D, 040, PicassoII; A4000D, A1200, Blizzard 030 MKIV - both not working :(
 

Offline psxphill

Re: Different AGNUSes 8372 vs 8375
« Reply #3 on: June 22, 2022, 09:03:45 AM »
 
The following users thanked this post: Tumbleweed

Offline BozzerBigD

Re: Different AGNUSes 8372 vs 8375
« Reply #4 on: June 22, 2022, 02:10:10 PM »
@Thread

Missed opportunity! This thread should be caled:

"Who has the Phatest Angus?"
 8)
"Art challenges technology. Technology inspires the art."

John Lasseter, Co-Founder of Pixar Animation Studios
 

Offline Tumbleweed

Re: Different AGNUSes 8372 vs 8375
« Reply #5 on: June 22, 2022, 04:05:07 PM »
@psxphill

Thanks for that doc. Very helpful.

Does anyone know whey there were so many revisions? The jump from 512k to 1MB to 2MB I can understand but why so many versions of the 2MB parts?

Im edging towards leaving the 8372 as is as its not clear what the advantages of the 8375 part are. I did find schematics for an an adapter board to use a 8375 in a A3000D but Ive not found anything yet to show what improvements the 8375 has over the 8372.

Much appreciated.

Weed
A3000T, Cybervision64, CSMKII 060; A3000D, PicassoII, Z3 Fastlane; A2000D, 040, PicassoII; A4000D, A1200, Blizzard 030 MKIV - both not working :(
 

Offline Matt_H

Re: Different AGNUSes 8372 vs 8375
« Reply #6 on: June 22, 2022, 05:23:18 PM »
Every 3000/3000T motherboard picture in the usual hardware databases has an 8372-series Agnus, so probably best to leave it.

As to why there were so many revisions? I can only guess, but probably some combination of FCC compliance, cost-reduction, and compatibility with new board revisions.
 

Offline Castellen

Re: Different AGNUSes 8372 vs 8375
« Reply #7 on: June 22, 2022, 08:38:20 PM »
I'd agree with Matt, many of the variants appear to accommodate specific Amiga models.  For example, later 8375 versions added a 14MHz clock output that was needed for Gayle that was used in the A600.  It also appears that they might have been trying to work around limitations of not quite having enough pins on the PLCC84 package to do everything.

Some variants of 8375 are the same die internally, but bonded differently to change functions of specific pins.  Have a look at this specification document: http://amiga.serveftp.net/Datasheets/390544-01_8375_Agnus_specification.pdf

Needless to say, many of the variants have different pinouts, so they're not always directly exchangeable.

I'm not aware of anything major that the 8375 'fixes' from the 8372.  Though I am aware of the many headaches I've had with repairing boards from customers who have helpfully decided to play "Agnus Roulette" by swapping out some random variant of the part, can't get the board working, and send it for repair, neglecting to mention that wee gem of information.  I then spend hours trying to figure out what's going on with it, eventually discovering the aforementioned game of roulette.  In addition to whatever the original fault was.

My advice is that if the current part is working, then don't mess with it.
 

Offline Matt_H

Re: Different AGNUSes 8372 vs 8375
« Reply #8 on: June 23, 2022, 12:47:57 AM »
I'd agree with Matt, many of the variants appear to accommodate specific Amiga models.  For example, later 8375 versions added a 14MHz clock output that was needed for Gayle that was used in the A600.  It also appears that they might have been trying to work around limitations of not quite having enough pins on the PLCC84 package to do everything.

Some variants of 8375 are the same die internally, but bonded differently to change functions of specific pins.  Have a look at this specification document: http://amiga.serveftp.net/Datasheets/390544-01_8375_Agnus_specification.pdf

Needless to say, many of the variants have different pinouts, so they're not always directly exchangeable.

I'm not aware of anything major that the 8375 'fixes' from the 8372.  Though I am aware of the many headaches I've had with repairing boards from customers who have helpfully decided to play "Agnus Roulette" by swapping out some random variant of the part, can't get the board working, and send it for repair, neglecting to mention that wee gem of information.  I then spend hours trying to figure out what's going on with it, eventually discovering the aforementioned game of roulette.  In addition to whatever the original fault was.

My advice is that if the current part is working, then don't mess with it.

I wonder if this explains some of the design choices of the 500+. Even a standard A500 can be made to use an 8372B 2MB Agnus with sufficient rework (Amazing Computing, February 1993). If Commodore had built a bunch of 8375s for the 600, maybe they designed the rev 8A to use the chips they had on hand rather than do another run of "obsolete" 1MB Agnus chips or do a run of pre-modified 6A boards and tap into the 8372-series stock intended for the 3000.
« Last Edit: June 23, 2022, 12:51:30 AM by Matt_H »
 

Offline Tumbleweed

Re: Different AGNUSes 8372 vs 8375
« Reply #9 on: June 23, 2022, 10:25:12 AM »
Towards the end Commodore were strapped for cash so maybe they used what the had out of necessity and used whatever parts they had available.

I think Ill stick with what I have - the only reason for considering tinkering was to potentially to improve stability.

I think the small niggle Ive got with he A3000T is it doesnt always boot up from powering on. A reset always resolves it and it boots fine. I think the issue may be caused by the Deneb card I have and potential DMA locking up as I also have a CV64 3D, CV64 and BigRam plus installed. I upgraded Buster to version 11 but I know there are limits to how many bus masters you can have at the same time. The Deneb is configured for DMA. I can force it to use PIO or Zorro II but that will slow down transfer rates accessing a USB pen drive I have plugged in.

Much appreciated.

Weed
A3000T, Cybervision64, CSMKII 060; A3000D, PicassoII, Z3 Fastlane; A2000D, 040, PicassoII; A4000D, A1200, Blizzard 030 MKIV - both not working :(
 

Offline mechy

Re: Different AGNUSes 8372 vs 8375
« Reply #10 on: June 24, 2022, 05:45:51 AM »
To my knowledge there is no speedup or stability change between 8372B (or AB) and 8375. Don't trust that list,i don't think the 8375 pinout matches the 3000/T machines. There was no pal only Agnus as far as i know for the 3000,they were always pal/ntsc capable. Only 8372B and 8372AB worked in the A3000/T.

Buster 11 only allows for 1 Bus Master. I think Buster 9 allowed multiple bus masters but was slower over all.

Hopefully Haynie comes thru with a Buster 12 some day!
« Last Edit: June 24, 2022, 05:48:51 AM by mechy »
 

Offline Tumbleweed

Re: Different AGNUSes 8372 vs 8375
« Reply #11 on: July 02, 2022, 06:22:04 PM »
This looks interesting.

https://www.buffee.ca/a-little-side-project/

A new Agnus

Weed
A3000T, Cybervision64, CSMKII 060; A3000D, PicassoII, Z3 Fastlane; A2000D, 040, PicassoII; A4000D, A1200, Blizzard 030 MKIV - both not working :(
 

Offline Matt_H

Re: Different AGNUSes 8372 vs 8375
« Reply #12 on: July 02, 2022, 08:38:21 PM »
This looks interesting.

https://www.buffee.ca/a-little-side-project/

A new Agnus

Weed

Nice! We need more projects like this to relieve supply constraints of the custom chips.
 

Offline scuzzb494

Re: Different AGNUSes 8372 vs 8375
« Reply #13 on: July 02, 2022, 10:44:56 PM »